1. Field of the Invention
The present invention relates to a toner quantity measuring method and a toner quantity measuring apparatus which measure the quantity of toner adhering on a belt-shaped image carrier which is stretched across a plurality of rollers, and an image forming apparatus which comprises such a toner quantity measuring apparatus.
2. Description of the Related Art
Among image forming apparatuses of the electrophotographic type, such as a printer, a copier machine and a facsimile machine, are those which create a toner image on a belt-shaped image carrier. For example, in an apparatus which is described in Japanese Patent Application Unexamined Gazette No. H11-258872, four process units are disposed along a transfer belt (belt-shaped image carrier) which is stretched across two rollers. Each process unit creates a latent image on a photosensitive member, and the latent image is developed with toner to thereby form a toner image. The toner images thus formed by these process units have different toner colors from each other (yellow, cyan, magenta, black), and transferred onto the transfer belt so that they are laid one atop the other. A color image is created on the transfer belt in this manner.
Further, in this apparatus, for the purpose of forming an image with a stable density by means of adjustment of the image densities of toner images, toner images having predetermined patterns (patch images) are formed on the transfer belt and the densities of these patterns are measured with a density sensor. The density sensor comprises a light emitting element which irradiates light upon the transfer belt and a light receiving element which receives light which is reflected by the transfer belt. A controller for controlling the apparatus calculates the quantity of toner adhering to the transfer belt based on an output from the light receiving element and accordingly measures the image densities of toner images.
By the way, there has not been any particular attention paid so far to the position at which the density sensor is arranged, and as a result, a sensor output contains various types of noise components and the accuracy of measuring a toner quantity deteriorates. In the conventional apparatus described above, for instance, since the density sensor is disposed at a position which is relatively far from the rollers, there are following problems.
At a position far from the rollers as described above, the transfer belt flaps in a direction which is approximately perpendicular to a direction in which the belt travels. Therefore, a distance (hereinafter referred to as xe2x80x9ca sensing distancexe2x80x9d) from the sensor to the transfer belt (belt-shaped image carrier) changes at random or in an instable manner, and a sensor output becomes instable because of the varying distance. This results in difficulty in conducting accurate measurement.
In addition, the transfer belt is stretched across the plurality of rollers and some rollers are eccentric to no small extent. Because of this, the transfer belt flaps even more as the eccentric rollers rotate, which makes a sensor output instable and accurate measurement difficult.
Further, the thickness of the transfer belt is not uniform all over the entire circumference of the transfer belt but may be uneven. This acts as one factor which changes the sensing distance.
Still further, the quantity of light which is reflected by the transfer belt is influenced not only by toner images formed on the transfer belt but by the condition of a surface of the transfer belt as well. Particularly when the condition of the surface of the transfer belt, e.g., the reflectance and the surface roughness, is not uniform, one can not ignore an influence by the surface condition.
A principal object of the present invention is to provide a toner quantity measuring apparatus and a toner quantity measuring method which allow to highly accurate measure the quantity of toner adhering to a belt-shaped image carrier in a structure that the belt-shaped image carrier is stretched across a plurality of rollers.
Another object of the present invention is to provide a surface condition detecting method which allows to precisely detect the condition of a surface of a belt-shaped image carrier such as a transfer belt and a photosensitive belt.
Yet another object of the present invention is to provide an image forming apparatus which forms an image with a stable density based on a result of measurement conducted with a toner quantity measuring apparatus or by a toner quantity measuring method.
The present invention is direct to an apparatus for and a method of measuring the quantity of toner adhering on a belt-shaped image carrier which is stretched across a plurality of rollers. The apparatus comprises: a sensor irradiates light upon the belt-shaped image carrier, and receives light reflected by the belt-shaped image carrier and outputs a signal which corresponds to the quantity of the received light; and toner quantity deriving means calculates the quantity of the toner adhering to the belt-shaped image carrier based on the output from the sensor.
The sensor comprises a light emitting element which irradiates light upon the belt-shaped image carrier. The light emitting element is positioned to face one of the plurality of rollers across the belt-shaped image carrier, and irradiates light upon a wind area, out of a surface area of the belt-shaped image carrier, in which the belt-shaped image carrier rests on a sensor-facing roller which is positioned to face the light emitting element.
The toner quantity deriving means samples an output signal from the sensor while the belt-shaped image carrier rotates and travels, calculates eccentric components of the roller based on a sampling output, removes the eccentric components from the sampling output and accordingly calculates a periodic profile which is indicative of the condition of a surface of the belt-shaped image carrier, and for calculation of the image density of a toner image on the belt-shaped image carrier, using the eccentric components and the periodic profile, the toner quantity deriving means corrects the output from the light receiving element which receives light reflected by the belt-shaped image carrier and calculates the image density of the toner image based on a correction value.
In the case that the length of the circumference of the belt-shaped image carrier is an integer multiple of the length of the circumference of one of the rollers, and the belt-shaped image carrier rotates one round while the one of the rollers rotates two or more rounds, before a toner image is formed on the belt-shaped image carrier, the toner quantity deriving means samples the output signal from the sensor while the belt-shaped image carrier rotates and travels and calculates eccentric components of the roller based on a sampling output. Thereafter, for calculation of the image density of the toner image on the belt-shaped image carrier, using the eccentric components, the toner quantity deriving means corrects the output from the sensor which receives light reflected by the belt-shaped image carrier and calculates the image density of the toner image based on a correction value.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.